Re: [PATCH v2 2/2] backlight: gpio: add support for multiple GPIOs for backlight control
From: Daniel Thompson <hidden>
Date: 2026-01-28 10:58:04
Also in:
dri-devel, linux-devicetree, linux-leds, lkml
On Tue, Jan 20, 2026 at 06:20:36PM +0530, Sudarshan Shetty wrote:
quoted hunk ↗ jump to hunk
The gpio-backlight driver currently supports only a single GPIO to enable or disable a backlight device. Some panels require multiple enable GPIOs to be asserted together. Extend the driver to support an array of GPIOs for a single backlight instance. All configured GPIOs are toggled together based on the backlight state. Existing single-GPIO Device Tree users remain unaffected. Signed-off-by: Sudarshan Shetty <redacted> --- drivers/video/backlight/gpio_backlight.c | 66 ++++++++++++++++-------- 1 file changed, 45 insertions(+), 21 deletions(-)diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c index 728a546904b0..11d21de82cf5 100644 --- a/drivers/video/backlight/gpio_backlight.c +++ b/drivers/video/backlight/gpio_backlight.c@@ -14,17 +14,29 @@ #include <linux/platform_device.h> #include <linux/property.h> #include <linux/slab.h> +#include <linux/bitmap.h> struct gpio_backlight { struct device *dev; - struct gpio_desc *gpiod; + struct gpio_descs *gpiods; + unsigned long *bitmap; }; static int gpio_backlight_update_status(struct backlight_device *bl) { struct gpio_backlight *gbl = bl_get_data(bl); + unsigned int n = gbl->gpiods->ndescs; + int br = backlight_get_brightness(bl); - gpiod_set_value_cansleep(gbl->gpiod, backlight_get_brightness(bl)); + if (br) + bitmap_fill(gbl->bitmap, n); + else + bitmap_zero(gbl->bitmap, n); + + gpiod_set_array_value_cansleep(n, + gbl->gpiods->desc, + gbl->gpiods->info, + gbl->bitmap); return 0; }@@ -48,26 +60,43 @@ static int gpio_backlight_probe(struct platform_device *pdev) struct device *dev = &pdev->dev; struct gpio_backlight_platform_data *pdata = dev_get_platdata(dev); struct device_node *of_node = dev->of_node; - struct backlight_properties props; + struct backlight_properties props = { };
This change is unrelated to the patch description. Do not "hide" changes like this. It you want to replace the memset() it's better to send a separate patch.
struct backlight_device *bl; struct gpio_backlight *gbl; - int ret, init_brightness, def_value; + bool def_value; + enum gpiod_flags flags; + unsigned int n; + int words; - gbl = devm_kzalloc(dev, sizeof(*gbl), GFP_KERNEL); - if (gbl == NULL) + gbl = devm_kcalloc(dev, 1, sizeof(*gbl), GFP_KERNEL); + if (!gbl)
Again, this change is unrelated to the patch description. Do not include changes that are not described in the patch description.
return -ENOMEM; if (pdata) gbl->dev = pdata->dev; def_value = device_property_read_bool(dev, "default-on"); + flags = def_value ? GPIOD_OUT_HIGH : GPIOD_OUT_LOW; + + gbl->gpiods = devm_gpiod_get_array(dev, NULL, flags);
How is it safe to transition from GPIOD_ASIS to GPIOD_OUT_LOW here? Forcing the backlight off if the default-on property is not present will prevent the backlight state being properly inherited from the bootloader.
quoted hunk ↗ jump to hunk
+ if (IS_ERR(gbl->gpiods)) { + if (PTR_ERR(gbl->gpiods) == -ENODEV) + return dev_err_probe(dev, -EINVAL, + "The gpios parameter is missing or invalid\n"); + return PTR_ERR(gbl->gpiods); + } - gbl->gpiod = devm_gpiod_get(dev, NULL, GPIOD_ASIS); - if (IS_ERR(gbl->gpiod)) - return dev_err_probe(dev, PTR_ERR(gbl->gpiod), - "The gpios parameter is missing or invalid\n"); + n = gbl->gpiods->ndescs; + if (!n) + return dev_err_probe(dev, -EINVAL, + "No GPIOs provided\n"); + + words = BITS_TO_LONGS(n); + gbl->bitmap = devm_kcalloc(dev, words, sizeof(unsigned long), + GFP_KERNEL); + if (!gbl->bitmap) + return -ENOMEM; - memset(&props, 0, sizeof(props)); props.type = BACKLIGHT_RAW; props.max_brightness = 1; bl = devm_backlight_device_register(dev, dev_name(dev), dev, gbl,@@ -81,21 +110,16 @@ static int gpio_backlight_probe(struct platform_device *pdev) if (!of_node || !of_node->phandle) /* Not booted with device tree or no phandle link to the node */ bl->props.power = def_value ? BACKLIGHT_POWER_ON - : BACKLIGHT_POWER_OFF; - else if (gpiod_get_value_cansleep(gbl->gpiod) == 0) + : BACKLIGHT_POWER_OFF; + else if (gpiod_get_value_cansleep(gbl->gpiods->desc[0]) == 0)
This logic is broken. This code path needs to be taken is *any* GPIO is low (and, as mentioned, the initial GPIO state must be GPIOD_ASIS).
bl->props.power = BACKLIGHT_POWER_OFF;
else
bl->props.power = BACKLIGHT_POWER_ON;
- bl->props.brightness = 1;
-
- init_brightness = backlight_get_brightness(bl);
- ret = gpiod_direction_output(gbl->gpiod, init_brightness);
- if (ret) {
- dev_err(dev, "failed to set initial brightness\n");
- return ret;
- }
+ bl->props.brightness = def_value ? 1 : 0;
+ gpio_backlight_update_status(bl);
+
platform_set_drvdata(pdev, bl);
return 0;
}Daniel.